The preferred embodiment concerns a method to reduce the curling of a printing substrate in a printer, in which at least one print region of the printing substrate is printed with ink. The preferred embodiment also concerns a device to print to a printing substrate with ink.
Moisture is introduced into the printing substrate via the application of the ink, such that moisture differences occur within the printing substrate. The more ink that is applied, the damper the printing substrate in this region. Furthermore, the moisture of the printing substrate depends on the material of the printing substrate, in particular the absorption capability of the material. In particular, paper is used as a printing substrate. The introduction of the moisture leads to a swelling of the fibers of the printing substrate in this region, such that tension differences in the printing substrate that lead to the formation of waves (what is known as “curling”) arise due to the moisture differences of the printing substrate. The quality of the print image is affected by the curling, and the travel behavior of the printing substrate web in the printer and in additional processing devices arranged after the printer is negatively affected. The swelled printing substrate also incites a poorer optical impression than a smooth printing substrate.
A known method to reduce the curling is to direct the printing substrate around rollers with relatively large radii, and to thus pull the waves out of the printing substrate. What is disadvantageous in this method is that it can hereby lead to folding. In order to avoid or to minimize this, rollers with large radius must be used, and the printing substrate must be directed so that it is advantageously deflected by angles less than 45°. This in turn has the consequence that a great deal of structural space is required, and the printer has a complex and costly design.
Inkjet recording methods in which a print image is applied with water-based ink on one side of the printing substrate are known from the documents EP 0 787 596 B1 and U.S. Pat. No. 5,764,263. The water-based ink also comprises a humectant and/or a curling preventative. On the opposite side, at the points at which the print image was applied, the same print image is applied with a clear fluid that comprises the same humectant and/or the same curling preventative. In the method it is problematic that the print image must be applied on both sides, and that special substances must respectively be added to the ink or clear fluid.